Sort the invoice customer dropdown alphabetically

[davidbucka]

Fixes #131

Problem

/api/v1/customers returns rows ORDER BY created_at DESC, and InvoiceEditor.svelte renders that order straight into the customer <select>. On both /invoices/new and /invoices/[id]/edit the dropdown is therefore ordered newest-first, which gets harder to scan as the customer list grows.

Change

One file. The customers derived value in InvoiceEditor.svelte now sorts a copy of the list by name, using the same localeCompare options the invoice table already uses in routes/invoices/+page.svelte:

String(a?.name || "").localeCompare(String(b?.name || ""), undefined, {
  numeric: true,
  sensitivity: "base",
})

Sorting client-side rather than in the SQL keeps the change scoped to the dropdown the issue is about. Changing ORDER BY in controllers/customers.ts would also flip the /customers listing away from newest-first, and SQLite COLLATE NOCASE is ASCII-only, so accented names would sort after Z. Happy to move it into the query instead if you would rather have it apply everywhere.

Testing

Ran the backend and the SvelteKit dev server locally with seven customers created in deliberately non-alphabetical order.

Before:

Charlie & Co, Ökotec Berlin, Ärzte Zentrum Nord, Beta Ltd, Müller AG, alpha services, Zeppelin GmbH

After:

alpha services, Ärzte Zentrum Nord, Beta Ltd, Charlie & Co, Müller AG, Ökotec Berlin, Zeppelin GmbH

Casing is ignored, so alpha services sorts first rather than last, and Ä/Ö sort next to A/O.

Also checked on /invoices/[id]/edit that the list is sorted while the invoice's existing customer stays preselected, and that picking a different customer from the sorted dropdown saves correctly.

bun run check reports 0 errors, eslint is clean, and bun run build succeeds. prettier --check flags the same 5 files it already flags on an unmodified main; the changed file passes.